That threshold seems a little low. If you reverse the scenario and have Gibson go north with the team, and suppose he puts up a 5+ ERA "in May" (early? late?), sending him down to AAA might seem premature, depending on fundamental factors and if he's showing signs of being able to improve. So I wouldn't fault a team for sticking with a veteran in that circumstance either. Pitchers have bad months or two and still turn the season around, if the hole they've dug isn't too deep. If they had a Jason Marquis situation with an 8+ ERA after 7 starts and didn't drop him (as they did in 2012) to give someone like Gibson a chance, that would be damning. They also did let Blackburn run up a 7+ ERA that season, in even more starts, and that would be even more damning in this situation now to keep Gibson down if he's performing.